using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace Utilities
{
    /// <summary>
    /// A class that manages a global low level keyboard hook
    /// </summary>
    class globalKeyboardHook
    {
        #region Varables
        /// <summary>
        /// defines the callback type for the hook
        /// </summary>
        public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);
        keyboardHookProc hookProcCallback;

        public delegate void KeyDownDelegate(int keyCode, bool Shift, bool Ctrl, bool Alt);
        KeyDownDelegate KeyDownCallback;

        public struct keyboardHookStruct
        {
            public int vkCode;
            public int scanCode;
            public int flags;
            public int time;
            public int dwExtraInfo;
        }

        const int WH_KEYBOARD_LL = 13;
        const int WM_KEYDOWN = 0x100;
        const int WM_KEYUP = 0x101;
        const int WM_SYSKEYDOWN = 0x104;
        const int WM_SYSKEYUP = 0x105;

        /// <summary>
        /// Handle to the hook, need this to unhook and call the next hook
        /// </summary>
        IntPtr hhook = IntPtr.Zero;

        private bool ShiftIsDown = false;
        private bool CtrlIsDown = false;
        private bool AltIsDown = false;

        public event KeyDownDelegate KeyDown;

        #endregion

        #region Constructors and Destructors
        /// <summary>
        /// Initializes a new instance of the <see cref="globalKeyboardHook"/> class and installs the keyboard hook.
        /// </summary>
        public globalKeyboardHook()
        {
            hookProcCallback = new keyboardHookProc(hookProc);
        }

        /// <summary>
        /// Releases unmanaged resources and performs other cleanup operations before the
        /// <see cref="globalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.
        /// </summary>
        ~globalKeyboardHook()
        {
            unhook();
        }
        #endregion

        #region Public Methods
        /// <summary>
        /// Installs the global hook
        /// </summary>
        public void hook()
        {
            IntPtr hInstance = LoadLibrary("User32");
            hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProcCallback, hInstance, 0);
        }

        /// <summary>
        /// Uninstalls the global hook
        /// </summary>
        public void unhook()
        {
            UnhookWindowsHookEx(hhook);
        }

        /// <summary>
        /// The callback for the keyboard hook
        /// </summary>
        /// <param name="code">The hook code, if it isn't >= 0, the function shouldn't do anyting</param>
        /// <param name="wParam">The event type</param>
        /// <param name="lParam">The keyhook event information</param>
        /// <returns></returns>
        public int hookProc(int code, int wParam, ref keyboardHookStruct lParam)
        {
            if (code >= 0)
            {
                int keyCode = lParam.vkCode;

                if (wParam == WM_KEYUP || wParam == WM_SYSKEYUP)
                {
                    switch (keyCode)
                    {
                        case 160:
                        case 161:
                            ShiftIsDown = false;
                            break;

                        case 162:
                        case 163:
                            CtrlIsDown = false;
                            break;

                        case 164:
                        case 165:
                            AltIsDown = false;
                            break;
                    }
                }

                if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null))
                {
                    switch (keyCode)
                    {
                        case 160:
                        case 161:
                            ShiftIsDown = true;
                            break;

                        case 162:
                        case 163:
                            CtrlIsDown = true;
                            break;

                        case 164:
                        case 165:
                            AltIsDown = true;
                            break;
                    }

                    KeyDown(keyCode, ShiftIsDown, CtrlIsDown, AltIsDown);
                }
            }

            return CallNextHookEx(hhook, code, wParam, ref lParam);
        }
        #endregion

        #region DLL imports
        /// <summary>
        /// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null
        /// </summary>
        /// <param name="idHook">The id of the event you want to hook</param>
        /// <param name="callback">The callback.</param>
        /// <param name="hInstance">The handle you want to attach the event to, can be null</param>
        /// <param name="threadId">The thread you want to attach the event to, can be null</param>
        /// <returns>a handle to the desired hook</returns>
        [DllImport("user32.dll")]
        static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc hookProcCallback, IntPtr hInstance, uint threadId);

        /// <summary>
        /// Unhooks the windows hook.
        /// </summary>
        /// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>
        /// <returns>True if successful, false otherwise</returns>
        [DllImport("user32.dll")]
        static extern bool UnhookWindowsHookEx(IntPtr hInstance);

        /// <summary>
        /// Calls the next hook.
        /// </summary>
        /// <param name="idHook">The hook id</param>
        /// <param name="nCode">The hook code</param>
        /// <param name="wParam">The wparam.</param>
        /// <param name="lParam">The lparam.</param>
        /// <returns></returns>
        [DllImport("user32.dll")]
        static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);

        /// <summary>
        /// Loads the library.
        /// </summary>
        /// <param name="lpFileName">Name of the library</param>
        /// <returns>A handle to the library</returns>
        [DllImport("kernel32.dll")]
        static extern IntPtr LoadLibrary(string lpFileName);
        #endregion
    }
}
